induction loop

Not that I can think of. If you used cat 5 UTP network cable you could get 8 turns.

No. the cancelling effect is only seen when equal currents flow in opposite directions - in the loop they are flowing in the same direction. A length of 25 pair phone cable cable would (if wired correctly) get you 50 turns and probably have an impedance in the ballpark of 8 ohms...

another trick is to use ribbon cable with IDC connectors (eg a 10 way cable and a set of DE9 plug and socket to make a 10-turn loop, just crimp one end with the cable offset by one position,

do they do transformers for those loops so you can just lay a single fat conductor round the perimeter?

Thanks